Measurement of cerebrospinal fluid (CSF) levels of the minor dopamine metabolite 3,4-dihydroxyphenylacetic acid in neonates and children indicates that a rapid decline (approximately 90%) occurs in the first 2 years of life. The much less rapid ontogenetic decline seen for the predominant dopamine metabolite, homovanillic acid (HVA), indicates that differing factors affect CSF levels of the two acid metabolites. Further study is required to determine which compound more closely reflects ontogenetic changes in dopamine functioning.